1. Technical Field of the Invention
This invention relates to a roller bit for use in drilling for the oil, natural gas, mine and geological drilling, and more particularly relates to a roller bit with the parallel inlayed compacts.
2. Prior Art
Roller bits have been widely used as a tool for earth boring. A roller bit usually consists of the cone and the head. The cone may be one or more, and the head is moveably attached an inner hole of the cone by a suspending-arm shaft at the lower part of the head, so that the cone can rotate around the shaft. The cutting structure of the outer surface of the cone crushes the rock formation under the action of the impact and the slide shearing generated by the combined movement of the cutting structure with revolution, self-rotation and the axial advancement of the cone.
The prior art roller bits are divided into two sorts which are a steel-tooth bit and a compact bit. The teeth and the cone of the steel-teeth bit are integrally formed, with a broad tooth cutting edge which can effectively scrape and chisel the soft earth formation, but when a hard formation is reached, the steel-teeth are easily worn with the result of losing their cutting function. Even when coated with an abrasion-resistant material, the steel-teeth still crack or break when they encounter hard formations. In a geological formation with stringers, where a steel-tooth bit cannot effectively drill through the hard formation, a compact roller bit must be used. The compacts of this kind of bit are usually made from carbide, with higher hardness which are more wear-resistant, but the cutting edge of the compact not as broad as in the steel tooth bit and cannot effectively drill into a soft formation.
From this we can see that the prior art steel teeth bit and compact bit both cannot be effectively applied for use on a formation with stringers. In order to overcome the above problems, U.S. Pat. No. 5,421,423 discloses a kind of roller cone bit having the oblate compact with a longer crest. Although it can be effectively applied to an earth formation with stringers, it has an interference fit between an oblate compact and oblate holes on the cone which require that the compact as well as the holes be machined with very high precision. The manufacture of such a roller bit and oblate compact is difficult, inefficient and not cost effective.
The object of this invention is to overcome the above problems and to provide a roller bit with parallel compacts which are easy to machine, but also low cost, and can drill through earth formation with stringers effectively.
The object of this invention can be realized by the following aspects: the roller bit according to present invention is constructed of head and cone. The cone has compacts for breaking the rock, and the head supports the cone. The lower part of the head has a cantilevered head shaft. The cone is mounted on the head shaft by means of a locking mechanism and a bearing couple which is between the cone inner hole and the head shaft permitting the cone to rotate around the shaft. Several compact lands and grooves are arranged on the cone. The compact lands are machined into several base teeth by milling, and two to three small cylindrical holes are parallelly machined at the top of the base teeth along the longitudinal direction of the teeth. The cylindrical compacts are inlayed into corresponding cylindrical holes, thus forming a roller-bit with a parallel inlayed compacts cutting structure.
According to the above aspects, a gap between the parallel inlayed compact may be 2 to 5 mm. The base of the compact is cylindrical in shape, which is interference fitted in the circular holes on the cone. The crest of the compact is wedge shaped, and has an elongated cutting edge. The teeth carrying the compact land can be the shape of a straight taper and straight teeth, or can be the shape of a spiral taper and spiral straight teeth. The spiral angle xcex1 is between 5 to 15 degrees to the generatrix of the cone.
The invention has the following advantages: 1. By employing parallel compacts, the cutting performance is similar to that of oblate compacts which have longer cutting edges. The noncontinuous long crest of compacts according to the invention are constructed so that it is easy to engage an earth formation and is thus helpful in improving rock breaking efficiency and the life of the bit. In addition, the teeth-groove and the annular separating groove create an advantage for chip removing, improvement of the cutting condition, and preventing bit balling; 2. By adopting a cylindrical body, it is not only easier to machine, but also creates high fitting precision, so that product quality can be guaranteed with low manufacture costs and good economy; 3. The roller bit according to the invention can drill through hard earth formations, and also break the hard earth formation with a scraping action, so it is effectively applied to earth formations with stringers, therefore increasing drilling efficiency.